Setting valve lash isn’t hot rod voodoo. It’s not some sort of mechanical magic or wrenching witchcraft reserved for the automotive illuminati either.
So why do some people seem so spooked when you bring up the topic of adjusting valve lash?
Proper valve lash, which is the clearance between the rocker arm and valve tip in pushrod engines, is a critical way to reduce valvetrain wear and ensure optimum performance. Lash adjustments can also help you tune your engine for more low- or top-end horsepower, depending on the lash settings. With so many potential benefits, hot rodders should embrace the idea of adjusting valve lash—not fear it!
As our friends at COMP Cams explain perfectly in this video, there’s no need to shy away from making valve lash adjustments. The job can be done right in your home garage with the proper tools—valve lash adjusting wrench and feeler gauges—and the procedure shown below.
No hot rod hocus-pocus required.
“Valve lash is the mechanical clearance in the valvetrain from the valve tip to the rocker in a pushrod engine using solid lifters. Excessive lash will cause noise in the engine and wear in the valvetrain, while lashing the valve too tightly will cause the valve to hang open and the cylinder won’t run. Instead of making compression, air will blow through the valve—thus, proper valve lash is critical to optimum engine performance.
We use EOIC, which stands for ‘Exhaust Opening Intake Closing.’ This is just one method, but there are others. The EOIC method works with any pushrod engine using solid lifters.
With the valve covers and spark plugs removed, screw the poly-locks of the rocker arms until they just finger tight. Then, rotate the engine until the exhaust pushrod on the cylinder you are working on begins to move upward. You’ll be looking for any rocker arm movement. This is the process of exhaust opening. At this point, you can adjust the intake because the intake valve will be closed, ensuring that the intake lifter is on the base circle of the cam. This is particularly important as you run the risk of hanging open a valve if lash is adjusted when the lifter is not in this position. Place a feeler gauge between the valve tip and the rocker arm. Tighten the poly-lock of the rocker arm until the proper lash is found. When you get to your preferred lash, hold the adjuster nut in place and set it with the inner screw using an Allen wrench. The poly-lock adjuster nut adjusts the amount of valve lash while the set screw locks it into place. Finally, tighten with an adjustable torque wrench until it clicks at 20 foot-pounds of torque. This tightens the adjuster nut to the inner set screw and ensures that they do not come apart.
The lash on most engines is set anywhere from .012 inches to .022 inches. Check your cam card for exact valve lash settings.
To set lash on exhaust, rotate the engine again until you see the intake valve open to full lift and start to come back up. Again, simply watch for rocker arm movement. You then can set lash for exhaust the same way you did with your intake valve.
Some engine builders and racers use valve lash as a tool for tuning at the track. Tighter lash gives an engine more bottom end or torque, while greater lash creates more top end or horsepower, which is typically made in the higher rpm range. However, lashing a valve too tightly can hang open a valve while excessive lash will decrease duration of lift—in essence, making a cam smaller. Again, it is critically important to make sure that the lifter is on the base circle of the camshaft so that you can set lash. If you have lift, the lash will be incorrect and you can hang open a valve.”